It is known to use mechanical post driving devices to achieve the driving of posts of relatively large cross-section into the ground during the construction of fences, guard railings, and the like. These prior art devices generally operate by use of a large, heavy hammer assembly which is raised and dropped on the post, striking the post, and thereby driving it into the ground at a desired site. Prior art post driving devices often are designed to be affixed to a vehicle, improving ease of use and allowing the user to quickly and efficiently place a large number of posts at the desired location during fence construction.
Prior art post driving devices, including those for which operation of the hammer assembly is achieved by means of hydraulic pressure or by a cable-type assembly, place the hammer lifting means at the rear of the hammer assembly between the post driver and the vehicle to which it is mounted. Prior art devices also often require the user to manually hold the post being driven in place during the initial strikes of the post driving operation, thereby increasing risk to the user.
Such devices, in general, are effective for their intended purpose. However, placement of the hammer lifting means at the rear of the hammer assembly results in certain disadvantages. In order to efficiently drive a post of relative large cross-section, the hammer assembly must be of relatively large weight and mass. Lifting and dropping such a hammer assembly using only a rear-mounted hydraulic cylinder or cable may result in significant tilting of the post driver during the striking operation due to the offset placement of the hammer assembly relative to the hammer lifting means.
Additionally, in order to be effective, the hammer assembly must be offset relative to the vehicle to which it is mounted, further contributing to the instability of the post driver. Accordingly, there is need in the art for a post driving device which overcomes this limitation in the prior art devices. There also is a need for a mobile post driver which obviates the need for a user to manually hold a post in place.